1. Field of the Invention
Apparatuses consistent with the present invention relate to demodulating a modulated ultrasonic signal to output an audible signal and playing an original audible signal, and more particularly, to a sound reproduction screen which receives an ultrasonic signal that is modulated to include an audible signal and demodulates the ultrasonic signal via a cell structure having nonlinearity.
2. Description of Related Art
An ultrasonic signal is a sound wave that has a frequency above 20 kHz, which is higher than a frequency of an audible signal. Generally, an ultrasonic signal as described above may not be perceived by humans, but may be modulated and transmitted including an audible signal. In this case, the range of an audible signal is extended in comparison to a general audible signal, and the directivity of a corresponding signal is also improved. Accordingly, an ultrasonic signal as described above is being utilized for various types of ultrasonic speakers.
Since a conventional ultrasonic speaker modulates an audible signal onto an ultrasonic signal and utilizes the modulated ultrasonic signal, the conventional ultrasonic speaker may transmit the modulated ultrasonic signal farther than a loudspeaker outputting a general audible signal and may also improve the directivity of a signal. Also, the conventional ultrasonic speaker operates in such a manner that, as modulated ultrasonic signals are passing through a medium such as air, audible signals from the modulated ultrasonic signals, demodulated due to nonlinear response characteristics of the medium, are output at a certain point. However, since the power of audible signals output at the point is a portion of the power of audible signals carried in ultrasonic signals, the conventional ultrasonic speaker must have a larger output than general loudspeakers. Accordingly, a listener is exposed to a sound field where ultrasonic signals are very powerful and those ultrasonic signals may cause physical harm. In this aspect, users have not readily utilized ultrasonic speakers as a sound source for listening and have utilized general loudspeakers that output frequency signals in an audible frequency band.
Accordingly, the present invention suggests a sound reproduction screen which utilizes a method of transmitting audible signals using ultrasonic signals and also demodulates modulated ultrasonic signals to output audible signals, and a new cell structure included in the sound reproduction screen.